In telecommunications, information is often sent, received, and processed according to the Open System Interconnection Reference Model (OSI Reference Model or OSI Model). In its most basic form, the OSI Model divides network architecture into seven layers which, from top to bottom, are the Application, Presentation, Session, Transport, Network, Data-Link, and Physical Layers, which are also known respectively as Layer 7 (L7), Layer 6 (L6), Layer 5 (L5), Layer 4 (L4), Layer 3 (L3), Layer 2 (L2), and Layer 1 (L1). It is therefore often referred to as the OSI Seven Layer Model.
Layer 2 is the layer which typically transfers data between adjacent network nodes in a wide area network or between nodes on the same local area network segment. Layer 2 provides the functional and procedural means to transfer data between network entities and might provide the means to detect and possibly correct errors that may occur in Layer 1. Examples of Layer 2 protocols are Ethernet for local area networks (multi-node), the Point-to-Point Protocol (PPP), HDLC and ADCCP for point-to-point (dual-node) connections. Layer 2 data transfer may be handled by devices known as switches.
To ensure high reliability and availability in communications networks, protection switching is often used. When implemented, protection switching typically provides a primary or “working” path for a network and a redundant or “protection” path for the network. Accordingly, each path may be monitored, and if a failure is detected on the working path, network traffic may be switched to the protection path. An example of protection switching may be Ethernet Linear Protection Switching (ELPS) as defined by the ITU G.8031 standard.
While protection switching may provide redundancy for link or path failures, it does not provide redundancy in the event of a failure of a network element (e.g., a switch) redundantly-interfaced to a point-to-point network. Accordingly, this disclosure provides for such network-element level redundancy.